Modern communication networks carry a plurality of different services, such as voice and data services. From a technical point of view, the role taken by the network, or a sub-network thereof, in carrying services can be considered as providing a network connection, wherein requirements as to availability and capacity of the network connection often depend on the type of service. Availability refers to the degree to which the network connection is in a specified state of operation suitable for the service, such as the existence of network connectivity at a specified capacity. Capacity refers to the data rate provided by the network connection. The actual physical routing path used in the network for providing the network connection is often subordinate for the service at an application layer and should be transparent to a user.
Adaptive Modulation (AM) applied to a link in the network, e.g., a link using microwave equipment, is an efficient tool to increase the capacity of the link. There is often a trade-off between availability and capacity. For example, a microwave link is planned for a small Bit Error Rate (BER) at a basic modulation level applied during a major part of its operation time, which results in approximately 99.999% availability of the link. Adaptive modulation means that in good radio conditions, the microwave channel is able to provide significantly higher capacity using higher modulation levels with lower availability. For example, the availability can decrease from 99.995% to 99.9% the higher the modulation level. A currently used modulation level thus depends on current radio channel conditions, such as a Signal-to-Noise Ratio (SNR). The automatic changing between modulation levels according to AM provides the highest available link capacity given the current radio channel conditions.
Different types of services have different Quality of Service (QoS) requirements including a minimum capacity and a maximum time of outage. In a double-connected network, for example using microwave links, it is possible to protect the services carried by the basic modulation level by a protection switching mechanism. When the link capacity is going down to zero, the protected traffic is rerouted to an alternative path, which does not contain the failed link. Herein, “failed” and “fault” refer to the outage of network connectivity. The Recommendation ITU-T G.8031/Y.1342 defines an examples of the protection switching mechanism in the context of Ethernet Operation, Administration and Maintenance (OAM). For example, in the context of voice telecommunication, services can tolerate only a short time of outage. Consequently, the rerouting, which is also referred to as switching, should be completed within a limited restoration time, for example within 50 ms.
Conventional protection switching mechanisms only detect the loss of connectivity, for example, because continuity check messages with high priority are used to probe the connectivity. A reduction in link capacity to an insufficient but non-zero capacity, for example due to AM, is not detected, although the service is already affected or even has collapses as a consequence of the insufficient reduced link capacity.
Other conventional techniques reroute services when it is not even necessary. When the link capacity is degraded, a predefined rerouting can be performed by default for some demands. However, if the actual traffic volume of a service is less than the degraded link capacity, rerouting is unnecessary and would add a futile workload for the network.
A possible solution for avoiding unnecessary service rerouting could base the rerouting decision on a measurement of both the actual traffic volume needed for the service and the actual link capacity available to the service. However, such measurements and their subsequent analysis take too long to fulfill the limited restoration time. Furthermore, the measurements require additional hardware equipment and software. Moreover, the measurements cause additional network traffic.